Sorry to hear about the damage. So, most survived?? Bleaching didn't seem to kill your coral. I thought it did. The bleaching in nature I thought was caused by high temperatures. So stress from any cause can cause bleaching?
There should be a clarification here. Bleaching is often misused to describe tissue necrosis in the media, but they are two very different things.
All stony corals have a white skeleton obviously which is covered by clear "flesh" or "skin" whatever you want to call it. Living in this "flesh" is millions of symbiotic single celled algae called zooxanthellae which come in numerous colors and in all photosynthetic corals provide a great deal of the energy the coral needs to survive. They are what give living corals their color.
Under stressful situations, often the zooxanthellae will die or be expelled by the coral leaving the clear tissue alive over the white skeleton giving a "bleached out" our transparent look. When favorable conditions return the algae can recolonize and give the coral back it's normal appearance. This is what bleaching is and what happened to the big coral in the center of the recent pics. For the most part, this isn't what's going on in the wild.
In the small polyped stony corals, or stick like corals if you will that most people think of when you say the word coral, what usually happens is tissue necrosis. Basically the "skin" dies and starts an avalanche effect spreading over the entire coral. The dead "skin" falls off the skeleton quickly leaving the bare skeleton behind giving a bleached look to an area where many corals are dead.
Basically the ones in the first pics are bleached out looking because they are bare skeletons of dead coral. All my small polyped stony corals (SPS) died in a couple days of tissue necrosis due to lack of oxygen since the water wasn't being constantly moved about them from the pumps. They are also strongly photosynthetic, but a week without light would have most likely only bleached them if they still had plenty of flow. Nearly all of the large polyped stony corals (LPS) survived, though some lost areas of tissue and the one bleached out but it's tissue is still alive and well. Half of my soft corals (no skeleton) made it, but of course my favorite one that can't be replaced as of now died.
Heat stress can cause bleaching and tissue necrosis, but that usually takes sustained temperatures over 90, which I've hit in the early days without any casualties. Corals are very similar to orchids in terms of basic needs, and it's hard to say what's going on in the wild that is killing so many of them.
Hope that clears it up a bit.
probably a few thousand $ lost. wouldn't even look at an aquarium for quite a while as he was heartbroken. corals are cool!
